From the fact that display quality is excellent, active matrix type liquid crystal display elements have been put on the market for portable terminals, liquid crystal televisions, projectors, computers and the like. In the active matrix type elements, thin film transistors (TFT), metal-insulator-metals (MIM), or the like are used for each pixel, and it is important that the liquid crystal compound or the liquid crystal composition used in this type has a high voltage holding ratio. In addition, a liquid crystal display element which includes a Vertical Alignment (VA) mode, an In-Plane Switching (IPS) mode, and an Optically Compensated Bend, Optically Compensated Birefringence (OCB) mode in combination is proposed in order to obtain wider viewing angle characteristics, and an Electrically Controlled Birefringence (ECB) mode reflective liquid crystal display element is proposed in order to obtain a brighter display. To comply with such liquid crystal display elements, new liquid crystal compounds or liquid crystal compositions are currently being proposed.
At present, as the liquid crystal display for smartphones, a fringe field switching mode liquid crystal display device (FFS mode liquid crystal display device) having high quality and excellent visual characteristics, which is a type of an IPS mode liquid crystal display element, is widely used (refer to PTLs 1 and 2). The FFS mode is a mode introduced for improving the low opening ratio and transmittance of the IPS mode, and as the liquid crystal composition used, a material using a p-type liquid crystal composition having positive dielectric anisotropy is widely used from the viewpoint of easily lowering a voltage. In addition, with respect to the FFS mode display element for portable terminals, there is a strong demand for more power saving, and liquid crystal element manufacturers are continuing to carry out active development in this regard, such as adoption of arrays using IGZO.
On the other hand, currently, it is also possible to improve the transmittance by changing a liquid crystal material currently using a p-type material to an n-type material having negative dielectric anisotropy (refer to PTL 3). This is because the FFS mode does not produce a perfect parallel electric field unlike the IPS mode, and in the case of using the p-type material, the liquid crystal molecules close to the pixel electrode tilt along the fringe electric field of the major axis of the liquid crystal molecules, thereby deteriorating the transmittance. On the other hand, in the case of using the n-type liquid crystal composition, since the polarization direction of the n-type composition is the minor axis direction of the molecules, the influence of the fringe electric field simply rotates the liquid crystal molecules along the major axis and the major axis of the molecule is maintained in a parallel arrangement, so that the transmittance does not decrease.
However, although an n-type liquid crystal composition is typical as a liquid crystal composition for VA, the VA mode and the FFS mode are different in all the points of orientation direction, electric field direction, and required optical characteristics. Further, liquid crystal display elements typified by the FFS mode are characterized by the structure of the electrodes as described later, the minimum value of an inter-electrode distance Rh in the horizontal direction between the pixel electrode and the common electrode is 0 and, even when the inter-electrode distance of vertical components Rv is added, the inter-electrode distance is as small as only the film thickness of the insulating film of the pixel electrode and the common electrode. Since the application voltage E has no large differences depending on the display element, the partial potential difference gradient is very large due to the small inter-electrode distance. In contrast, in the VA mode, since the common electrode and the pixel electrode have electrodes on both of the two substrates, the distance between the two electrodes does not become smaller than the cell gap of the liquid crystal cell. Accordingly, the potential difference gradient in the VA mode differs in that it is larger than that of the FFS mode display elements or the like in which the inter-electrode distance is small. The magnitude of the potential difference gradient due to the inter-electrode distance has a large influence on the design of the display element, and nothing is known about problems such as burn-in or drip mark for which it is difficult to predict the effects from the related art. Accordingly, even if the liquid crystal composition used for VA is simply used for this purpose, it is difficult to form a high-performance liquid crystal display element as required today, and there is a demand to provide an n-type liquid crystal composition optimized for a display element having a large potential difference gradient due to the distance between electrodes in the FFS mode or the like.